1. Field of the Invention
This invention relates to systems and methods for determining a location of a visual link to digital media on physical documents, and more particularly to calculating and adjusting a size and location of a visual digital media link based on the location of other digital media links and the similarities between portions of content on the media.
2. Description of the Related Art
There are many systems that provide links to digital media from physical media—such as a paper document—using visual content analysis and indicators. Typically, a user takes a picture of the document that includes a visual link using a cell phone or other portable device with a camera, and the image is processed either on the phone or a remote server to identify and then access the linked media. The linked media is then displayed on the phone.
One example of a visual link is an Embedded Media Marker (EMM) 100, illustrated in FIG. 1A. An EMM 100 differs from other content-based retrieval methods by placing a faint mark on a paper document indicating a specific region of the page to be captured without interfering with the readability of the page content. The EMM 100 may be represented by a boundary 102, icon 104 and a pointer 106. FIG. 1B illustrates an EMM 100 as it would appear on a paper document 104. The use and functions of EMMs are described in co-pending US Application No. 12/646,841, filed December 23, 2009 and incorporated herein by reference in its entirety. The EMMs not only indicate to the user that there is media associated with a part of the document, but also allows the user to zoom in with the camera to avoid capturing the rest of the page. By only indexing page regions, this approach reduces the size of the index for the document and provides a means to control retrieval accuracy by assuring the marked region on the page can be easily recognized.
The existing EMM system includes an authoring tool for placing an EMM on a document page that allows the user to interactively select a region of the page that is meaningful for EMM placement, and that has a number of keypoints for recognition. A keypoint is a feature vector describing the local image characteristics near a location in an image. As the user moves the EMM to desired locations, the capture region is dynamically increased or decreased based on the number of document keypoints. If there are insufficient keypoints, the EMM signified region of the page is shaded red. Although this prevents the user from placing an EMM in a region with too few keypoints, it does not guarantee recognition accuracy, since the keypoints might be similar or identical to other EMMs in the database.
While the current authoring tool in the EMM system checks if there are enough keypoints in a candidate region for an EMM, it does not check if those keypoints would conflict with previously authored EMMs or if the keypoints could be easily confused with content on other pages in a collection.